The invention relates to a method and an apparatus for producing an elongated filler from fibers, especially tobacco fibers. More particularly, the present invention relates to improvements in cigarette making machines and methods for producing cigarettes therein.
It is already known, particularly in the cigarette making industry, to form a stream from fibers, to advance the stream, to equalize the advancing stream by removing the surplus of fibers therefrom, and to densify and wrap the equalized stream to thereby form a filler (such as a cigarette rod from which individual cigarettes are to be severed). It is further known to control the removal of the surplus of fibers in dependence on a signal which is indicative of a parameter of the stream upstream of the equalizing location.
A conventional apparatus which is capable of performing such method includes a conveyor on which the stream is formed and by means of which the stream is advanced, an equalizer which removes the surplus of fibers from the advancing stream at a trimming station, a device for densifying the stream downstream of the equalizer and for wrapping the densified stream into a web, a device for monitoring a parameter of the stream upstream of the equalizing location, and a control arrangement which varies the distance between the equalizer and the conveyor in response to signals transmitted by the monitoring device.
The term "densification" is intended to denote the transformation of the equalized but unwrapped stream into its final shape with a cross section matching that of the wrapped tobacco filler (or cigarette rod) from which the individual cigarettes are severed on a continuing basis. Such conversion or transformation is performed by a so-called format garniture or wrapping mechanism wherein the tobacco is compressed during its passage therethrough and which, consequently, acts as a densifying arrangement. However, in the event that the tobacco in the tobacco stream is already considerably compressed during advancement to the equalizing location and/or the wrapping mechanism (for instance, by subjecting the tobacco stream, through the air-permeable conveyor advancing the same, to a pronounced suction), it can happen that the cross section of the equalized tobacco stream is the same or even smaller than the cross section of the cigarette rod. In this case, the expression "densification" is intended to mean the transformation of the tobacco filler into a body having the cross section of the wrapped cigarette rod. It is known to control the removal of tobacco fibers from a stream in dependence on the flow resistance of the stream. The signal denoting the resistance is formed in dependence on an air stream which is passed through (drawn) transversely of the tobacco stream upstream of the location of removal of surplus tobacco. The removal of the surplus is controlled by the signal in the sense of maintaining the flow resistance at a constant value.
It is further known to scan the surface of the tobacco stream by means of a photoelectronic system employing a roller which is pressed against the stream with a predetermined force and monitors the degree of densification which is dependent on the filling force of the tobacco. The signal then again serves to control the removal of tobacco fibers in the sense of maintaining the rigidity or hardness of the densified tobacco filler (cigarette rod) at a constant value.
Finally, it is known to photoelectronically sense the height of the tobacco stream and to control the so-called distributor of a cigarette making machine in dependence thereon, in order to maintain the height at a constant value. The surplus of tobacco fibers or shreds is removed from the tobacco stream for the purpose of maintaining its height at a constant value.